1. Field of the Invention
The present invention relates to a motorcycle fuel tank and more particularly relates to a motorcycle fuel tank made of aluminum or an aluminum alloy.
2. Description of the Related Art
To decrease the fuel consumption of a motorcycle or an automobile while improving its running performance, it is important to reduce the weight of its body as much as possible. The weight of a motorcycle or an automobile may be reduced by using a lighter weight material for its components. In the prior art, the majority of those components, including a frame, a chassis and so on, have been made of either iron or a steel containing iron. Recently, however, it was proposed that aluminum, having a smaller specific gravity than iron, be used as a material for those components. The density of aluminum is about one-third of that of iron. Thus, if aluminum or an aluminum alloy were used as a material for the components, then the weight of a motorcycle or an automobile could be reduced significantly.
Japanese Patent Application Laid-Open Publication No. 8-232789 discloses a fuel tank made of aluminum or an aluminum alloy for use in cars. This fuel tank includes an upper casing and a lower casing, which are made by a drawing process and which are brazed together, thereby defining a box-shaped closed space.
However, nobody has ever proposed a motorcycle fuel tank made of aluminum or an aluminum alloy. This is probably because a motorcycle fuel tank needs to meet a greater number of requirements than a car fuel tank and because it is not easy to obtain a fuel tank satisfying all of those requirements.
More specifically, as to motorcycles, the fuel tank forms an integral part of the vehicle's appearance, and therefore, needs to have a beautiful shape of good design. Also, in assembling the components on the body, the motorcycle fuel tank has to be arranged within a limited space. For that reason, a motorcycle fuel tank normally has a complex shape and it is difficult to make a tank of such a complex shape of an aluminum alloy, which is a metal that is hard to form in a desired shape and bond together. Furthermore, a motorcycle is easily subject to the vibrations of the wheels on the road, the vibrations of the engine, and the heat of the engine, and therefore, its fuel tank should be sufficiently durable so as to be protected from those vibrations and the heat. Furthermore, to fix a fuel tank of such a complex shape onto the frame of a motorcycle, it is necessary to provide a fixing portion for the fuel tank. However, the motorcycle fuel tank has such a complex shape that it is usually hard to provide a fixing portion for the motorcycle fuel tank with high positioning accuracy. Besides, this fixing portion also needs to be durable so as to be protected from the vibrations and heat from the motorcycle.